Summer 1999

Long-term use of marijuana does not lead to a decline in mental function,
according to researchers at the Johns Hopkins University (JHU) in Baltimore.
Individuals who confessed to having smoked marijuana, even heavily, have
no more signs of impaired mental function than people who have never used
cannabis (Constantine G. Lyketsos, et al., "Cannabis Use and Cognitive
Decline in Persons Under 65 Years of Age," American Journal of Epidemiology,
May 1999, vol. 149, p. 794-800; "Long-term Use Doesn't Hurt Mind, Study
Says," Detroit Free Press, May 7, 1999; "The Straight Dope," Science
News (US), May 22, 1999).

Scientists at JHU tracked the mental functioning of 1,318 Baltimore
residents aged 18 to 64 over the course of 11 ½ years. After analyzing
data gathered by the Mini-Mental State Examination, or MMSE, researchers
concluded that there is no cognitive decline associated with marijuana
use. The researchers said that cognitive decline is related to aging and
starts in individuals younger than 30 years old. The decline is said to
increase exponentially with each decade that passes, but attaining a higher
level of education may reduce the severity of cognitive decline.